ENSLAVED PLANTS 339 
the form of lichens have already been described (Sect. 331). 
It is not correct to describe the condition of such alge 
as slavery if the term is meant to imply that they derive 
no benefit from the association. Perhaps serfdom is a 
» Fie. 236. — Roots of Red Clover with Tubercles. 
l, sections of ascending branches ; 6, enlarged base of stem ; ¢, root-tubercles 
containing bacteria. 
more suitable word, though it is not the term used by 
botanists. At all events, the alga is enclosed within a 
network of fungus hyphe from which it cannot readily 
escape, and there does most of the work of the lichen, 
including all of the manufacture of food from carbon 
dioxide. 
